Method of making square-head screws



Dec. 17, 1935. H. MOORE 2,024,593

METHOD OF MAKING SQUARE HEAD SCREWS Patented-Dec. 17, 1935 UNITED STATESPATENT OFFICE METHOD OF MAKI G SQUARE-HEAD SCREWS This invention relatesto an improved method of making screws having square heads or heads ofother polygonal shapes, the method being more especially adapted to bepracticed with automatic machinery for carrying out the several steps inthe making of screws.

It is an object of the invention to make squarehead screws withoutheating the stock, and to make them in such a manner that they will besubstantially free from internal weakness and from excessive variationin the shape and dimensions of the head.

For a more complete understanding of themvention, reference may be hadto the description thereof which follows, and to the drawing of whichFigure 1 is a perspective view of a typical square-head screw madeaccording to the invention. a

Figure 2 is a fragmentary elevation of wire stock from which thefinished screws are made.

Figure 3 is an elevation, partly broken away to show in section, of ascrew'at an intermediate stage of its production.

Figure 4 is a fragmentary sectional view of mechanism for swaging thehead of a screw.

Figure 5 is a section on the line 5-5 of Figure 4;

Figure 6 is a fragmentary section similar to Figure 4, showing the partsin a different position of operation.

Figure '7 is a section on the line 1-1 of Fig- .ure 6.

erably employed, a piece of such stock being illustrated at H] in Figure2. The stock may be cut as at H to provide a blanklZ of predeterminedlength just suflicient for the finished screw. An end portion of theblank I2 is then swaged by suitable mechanism well known in the art toform a mushroom head l3 having a top face M which is flat or nearly so,and a rounded shoulder [5. This mushroom head is formed preferably priorto the formation of any screw thread on the shank of the blank. The headI3 is of substantially greater diameter than the shank, so that theheaded blanks can readily be fed into an automatic thread-cuttingmachine. In swaging the end portion of the blank l2 to form the head E3,the volume of the head is carefully predetermined so as to be justsufficient to form thehead-of the finished screw.

After the formation of the mushroom head [3 on'the blank 12, ascrew'thread lBis cut or otherwise formed on the shank of the blank l2.The blank is then ready for the final step of pressing the mushroom headlaterally at spaced points so as to swage the head into a'shape havingan approximately polygonal cross section, preferably square. Thisoperation is preferably performed while the blank is cold. To this end,the blank may be inserted in a suitable hole I! in a holder l8.Associated with the holder l8 are pressing members 2!], the hole I!being of such a depth that the mushroom head 13 is in correct positionfor engagement by the pressing elements 20. In the apparatus illustratedon thedrawing, four pressing elements 20 are illustrated for theformation of a square-headed screw, but it is evident that any desirednumber from two up can be employed to form heads having a plurality offlat side faces. In order to hold the blank in place in the hole I!during the pressing operation, a spring-pressed plunger (not shown)preferably bears on the top face it of the mushroom head, this plungerbeing adapted to yield readily, so that, when the head is swaged, theaxial flow of the. metal is not impeded by the yielding plunger. Whenthe blank is properly in position as illustrated in Figures 4 and 5, thepressing elements 20 are forced to the position illustrated in Figures 6and 7, these pressing elements engaging the mushroom head l3 laterallyat spaced points. The pressing elements 2% form fiat faces on the sidesof the head and swage the head into the approximate square shapeillustrated at 22 in Figures 6 and '7.

The size and shape of the mushroom head are preferably such that, whenthe sides are pressed a the mushroom head It. Hence, since the volume ofthe head is unchanged by the swaging operation, the axial length of thesquared head must be greater than that of the mushroom head. Thisincreased axial length of the head results from an axial flow of themetal as the mushroom head is laterally pressed. This operation is suchas to create no internal faults in the screw, the head of the screw thusformed being fully as strong as those of screws made by previously knownand practiced methods.

I claim:

1. A method of making a screw, which comprises swaging an end portion ofa piece of wire stock of predetermined length to form a mushroom headhaving a predetermined volume just suflicient for the head of thefinished screw, forming a screw thread on the shank of said piece, andthereafter cold-pressing the sides of said mushroom head simultaneouslyat a plurality of spaced points to swage the head into a polygonal shapehaving an increased axial length and a minimum cross-sectional dimensionsubstantially equal to the'dimension of the shank.

2. A method of making square-headed screws,

which comprises swaging an end portion of a piece of wire stock ofsuitable length to form a mushroom head of predetermined volume justsuflicient for the head of the squared head to be formed,screw-threading the shank of said piece of stock, thereafter supportingthe threaded piece so as to be capable of yielding axially, andcold-pressing the head of the piece laterally at four spaced points toform a squared head having a diagonal substantially equal to thediameter of the mushroom head before the pressing operation and aminimum diametrical dimension substantially equal to the diameter of theshank.

HARRINGTON MOORE. l5

